Fig. 3. (a-c) Fe-nutritional status and leaf chlorophyll levels (SPAD values) of soil-grown barley plants at 28 days after sowing (DAS), depending on Fe supply and atmospheric CO2 concentration. Bars represent means and standard errors. Different letters indicate significant differences at the P < 0.05 level. The dashed line symbolizes the average Fe concentration sufficient for average plant growth (Marschner, 1995).